Qualitative characterization of the endogenous cytokinins in red pine and aspects of their influence on seedling development.

摘要

Red pine seedlings alternate between root and shoot production in a periodic fashion. This habit is referred to as episodic growth and is assumed to be controlled by endogenous plant growth regulators. This project was concerned with the role played by cytokinins in the control of episodic growth.; After confirming the existence of episodic growth in red pine seedlings, a carrier solution was optimized and a series of exogenous application trials was conducted. Only those solutions containing a surfactant and N{dollar}sp6{dollar}-benzylaminopurine (BAP) produced an observable response. Foliar applications of BAP induced the formation of an apical cluster of buds. As the BAP concentration was increased from 2.5 to 200 mg/l, there was a corresponding increase in the number of buds formed. Hypocotyl length and the percentage of the induced buds that elongated were inversely proportional to the BAP concentration used. The response to BAP, as affected by seedling age and application number, was also determined. The younger the seedlings were when they received their first BAP treatment and the more applications they received, the greater the reduction in hypocotyl growth. As the number of BAP applications increased, the number of buds formed was proportionately greater. As the age at which seedlings received their first treatment of BAP increased, the percentage of buds that elongated decreased. When the same carrier solution, containing 200 mg/l BAP, was applied to the potting mix in which the seedlings were grown, axillary bud development along the hypocotyl was promoted. Germinating seeds were also treated with the same solution. Longer exposure to BAP resulted in progressively shorter hypocotyls and needles and in lower survival.; The origin of the buds induced by BAP was characterized histologically. The BAP treatments were found to induce precocious axillary bud development and adventitious bud formation. The suitability of this bud cluster for micropropagation of red pine was also explored.; Because the CKs produced by red pine have never been identified, they were qualitatively characterized. The cytokinins produced by roots and shoots were identified based on the retention times of biological activity on Sephadex LH-20 and Spherisorb ODS-2. Zeatin and zeatin riboside (ZR) were both found in the basic fraction of root and shoot extracts. The presence of ZR in both tissues was confirmed by GC-MS analysis. Evidence for the presence of dihydrozeatin O-glucoside in the shoot basic fraction and for zeatin O-glucoside in the roots is also presented. Zeatin riboside monophosphate, isopentenyladenosine monophosphate (iPMP) and glucosyl phosphate derivatives were found in both root and shoot acidic fractions. The presence of iPMP in both tissues implies that cytokinin biosynthesis is occurring throughout the plant. Evidence suggesting the presence of a phosphorylated derivative of zeatin O-glucoside in the roots is presented.